Professor Sings at Indonesia Rally. He Faces 4 Years in Jail for Defaming Army.

JAKARTA, Indonesia — The professor sang an old anti-army song at a rally outside the state palace in central Jakarta, Indonesia’s capital. After a video of his performance appeared online, the police arrested him this month for insulting a state institution.

A week earlier, a housewife in Surabaya was sentenced to 10 months in jail over four WhatsApp messages that a local company found insulting. She denied even sending the messages, which were in Javanese, a language she does not speak.

Both the professor, Robertus Robet, and the housewife, Saidah Saleh Syamlan, were charged under Indonesia’s sweeping online criminal defamation law, which allows anyone to file a complaint and carries a sentence of up to four years in prison.

Human rights advocates call the law overly broad and say it is used by government officials and influential people to stifle free expression.

“Cracking down on dissidents has reached an alarming level in Indonesia,” said Usman Hamid, Amnesty International’s executive director for Indonesia. “Regular citizens face charges for peaceful opinions posted on social media platforms.”

By some measures, Indonesia has become one of Asia’s more democratic countries since the fall of the military dictator Suharto in 1998. Every five years, Indonesia holds the world’s largest direct presidential elections. Next month, President Joko Widodo, a former furniture manufacturer, will again face his 2014 opponent, Prabowo Subianto, an ex-general and Suharto’s son-in-law.

But at the same time, the authorities stifle free expression by enforcing the criminal defamation law against citizens who protest government policies, complain about company practices or take offense at sexual harassment in the workplace.

The online defamation law was adopted in 2008 and initially allowed the police to jail suspects before trial. It was amended in 2016 reduce the maximum sentence from six years to four and eliminate the practice of pretrial detention.

The number of cases filed by the police peaked at 83 in 2016 and declined to 22 last year, according to the Southeast Asia Freedom of Expression Network, which monitors online speech and digital rights in the region.

Even so, rights advocates say the law remains a potent limitation on free speech because anyone can file a case with the police and a conviction can be based on flimsy evidence.

Sometimes the law targets a victim of abuse rather than the perpetrator.

A high school bookkeeper, Nuril Maknun, who recorded a lewd phone call from her boss that was circulated among a handful of people online, was sentenced in November to six months in jail for defaming him. She also spent two months in jail awaiting trial.

The use of criminal defamation is widespread in much of Southeast Asia, including in Myanmar,Singapore,Cambodia and Thailand, where governments often seek to limit public criticism. Human Rights Watch and Amnesty International have called for the repeal of all criminal defamation laws.

“For those with wealth and connections, hitting opponents with criminal defamation charges is a quick and easy way to seriously impair mounting public challenges and criticism,” said Phil Robertson, the deputy Asia director for Human Rights Watch. “In one fell swoop, an activist can lose their freedom, face damaging allegations difficult to refute and feel thoroughly intimidated.”

Civil defamation laws also are used in many countries to silence critics by imposing stiff fines or other financial penalties. But criminal defamation can land defendants in jail for years in addition to ruining them financially.

Mr. Robet, a longtime activist and a co-founder of Amnesty International Indonesia, took part in protests during the 1990s seeking to topple Suharto’s military government.

Now a sociology professor at State University of Jakarta, he attended the rally outside the presidential on Feb. 28 to protest unresolved cases of human rights abuses and a proposal to give army generals civilian posts in the government.

At the rally, he performed a rendition of a protest song that was popular in the Suharto era and sung by thousands of people at anti-Suharto demonstrations. Parodying an old army song, its lyrics call the military useless and say it should be disbanded.

Mr. Robet said that it was the first time in two decades that he had sung it in public, and that his goal was to call attention to the military’s growing influence.

His arrest would appear to prove his point.

“I sang this song to tell the new generations of the vibrant era of the civilian and student movement in 1998,” he said by email. “This is the irony. During the Suharto era, nobody got arrested for singing this song.”

After the video of him singing was posted online, former and current military officers complained.

The police arrested him at his home after midnight on March 7 and charged him with criminal defamation and insulting an authority or public institution. He was released later that day. The police handed the case to prosecutors last week.

Mr. Robertus questioned why he would be charged with online defamation since he had nothing to do with producing the video, posting it or circulating it online.

Amnesty International called on the police to drop the charges.

“This is a blatant and ludicrous attempt to intimidate and silence Robertus for his peaceful criticism of the military,” Mr. Usman said. “He is an academic who is guilty of nothing more than voicing his views over proposals to place senior military officers in positions of power within the government.”

The case against Ms. Saidah and the four WhatsApp messages dates to 2017.

The brief messages were sent using a SIM card that had been registered in her name. Sent to local bankers, they questioned the credibility of the company, PT Pisma Putra Textile, that had long employed Ms. Saidah’s husband, Aziz Hamedan, who retired as the company’s finance director in 2016.

The company, which manufactures sarongs, complained to the police that the messages were insulting. Officers questioned Ms. Saidah and Mr. Aziz. Both denied sending the messages.

Ms. Saidah said she had lost her phone and canceled her cellphone number before the messages were sent.

The police and prosecution were unable to find the phone or establish who possessed the SIM card at the time.

The defense argued that she could not have been responsible since she does not speak Javanese, the language used in the messages.

Nevertheless, on Feb. 26, the court found her guilty of defamation and sentenced her to 10 months in jail.

She remains free pending an appeal.

“It is shocking that people like Syamlan can go to prison on the basis of vague and severe criminal defamation laws compounded by questionable evidence,” said Andreas Harsono, an Indonesia researcher at Human Rights Watch.

He called on the Indonesian government to replace criminal defamation laws with a civil law that allows people with defamation complaints to sue for monetary damages.

“Sending someone to prison on flimsy evidence for sending WhatsApp messages critical of a company will have a disastrous and chilling effect on free speech,” Mr. Harsono said.